Operation of coke ovens and the like



July 18, 5 LL OPERATION OF COKE OVENS AND THE LIKE Filed Dec. 19, 1928 4 Sheets-Sheet l INVENTOR BY Q 7 DI EM Q Q ATTCR N EYS July 18, 1933. S P MILLER 1,918,709

OPERATION OF COKE OVENS AND THE LIKE Filed Dec. 19, 1928 4 Sheets-Sheet 2 Fig-L r' ,2 2... 5/ INVENTOR 1 J MMM 301 I ATTORNEYS 4 Sheets-Sheet 3 s. P. MILLER OPERATION OF COKE OVENS AND THE LIKE Filed Dec. 19, 1928 July 18, 1933.

INVENTOR 4a: V -a J, ATTORNEYS y 18, 1 5. P. MlLLER 1,918,709

OPERATION OF COKE OVENS AND THE LIKE Filed Dec. 19, 1928 4 'SheetST-Sheet 4 fik INVENTOR flmwfm ATTORNEYS *1 the tar as thus Patented July 18, 1933 entree STATES PATENT OFFICE STUART PARMHL'EE MILLER, OF ENGLEWOOD, NEW JERSEY, .ASSIG NOR TO THE BARRETT COMPANY, OF NEW YORK, N. Y., A CORPORATION 01 NEV JERSEY ornaarroiv or coim'ovnns AND THE LIKE Application filed December 19, 1928. Serial No. 326,924.

This invention relates to the operation of coke ovens and other coal distillation plants and particularly to the production of pitches having varying characteristics from the gases escaping from the ovens.

In the ordinary operation of by-product coke ovens the gases produced by the coking operation pass from the individual ovens through uptake pipes and goose-necks to a collector main common to the ovens of the battery. ovens at high temperature, e.g. 550 to 700 C. or higher, are cooled ordinarily as rapidly as possible by the application of:- sprays of ammonia liquor or ammonia liquor and tar in the moss-necks and collector main. The rapid cooling causes the sep-- aration of tar containing the heavier oils in the collector main. Further cooling is eli'eet ed in the cross-over main which connects thecollector rain to the condensing system and an additional quantity of tar carrying both heavier and lighter oils is thus separated. The collected tar is ordinarily shipped from the coke-oven plant to a tar-distillation plant for distillation and separation of the oils and the production of pitches or varying qualities.

The pitches produced by distillation of recovered contain ordinarily a proportion of tree carbon. Theydo not, however contain such a proportion of free carbon to make them available for certain uses for which pitches having a high tree carbon content are required. Such pitches are obtained ordinarily by the distillation of gas retort is of which only a limited ouan tv is avalable, or by the distillation 6r blended mixtures comprising such'retort tars. Similarly, the product of distillate tion of coke-oven tars contains too high a content of tree carbon to permit use thereof for certain other purposes where a low tree carbon content is essential. Pitches of low tree carbon content are obtained ordinarily by distillation of water-gas tar. There considerable demand in the trade for pitches of both low and high free car- The gases which leave thev inand. Consequently the production of both low and high free carbon content pitches from the operation of coke ovens is desirable and it is the general object of the present invention to provide a method and apparatus whereby such pitches can be recovered in an economical manner from the gases delivered from a coke oven.

During the operation of a coke oven the gases discharged contain a greater or less proportion of tar constitutents, depending upon the stage of the coking operation, and the tar constituents vary in their content of free carbon. Thus, during the earlier'part of the coking operation the gases contain a relatively larger proportion of tar constituents and are referred to commonly as rich gases The tar separated from such rich gases is low in free carbon. During the latter part of the coking operation the gases contain a lower proportion of tar 0011- stituents and are generally designated lean gases. The tar separated from such gases is high in free carbon. The coke ovens of a battery are operated in cycles so that difierent ovens are in different stages of the distillation operation, and normally the rich and lean gases are delivered indiscriminately to the collector main and treated in the manner hereinbefore described to separate tar and oils therefrom.

It is the particular object of the present invention to provide a method permitting the recovery of pitches of different characteristics, and especially the preparation of a high carbon road tar or pitch by the distillation of the tar y or pitch constituents which separate in a lean collector main of a coke oven battery by utilizing the hot cokeoven gases to heat and distill the tar or pitch. pitch may be accompanied by the production of clean oils directly by cleaning and then cooling the gases and vapors resulting from the distillation.

By alean gas collector mainI mean that main of a coke oven battery or other coal distillation system equipped with two as Where desired the production of or more gas collector mains, which is em 'ployed for collecting gases from the latter part of the coking operation in the various ovens or retorts of the coke oven battery or other coal distillation systems. The gases from the latter part of the coking operation are commonly called lean gases to distinguish them from the rich gases given oil during the early stages of the coking operation.

In carrying out the invention the rich and lean.gases from the individual ovens of a coke oven battery, for example, are

rected into separate collector mains, each of which is connected to all or a certain number, e.g., twenty, of the ovens of the battery through suitable uptake pipes and goosenecks, valves being provided to permit diversion of the gas at the appropriate time into the selected main depending upon the character of the gas which issues from the ovens' Thus, during the early stages of coal distillation in any particular oven the gases will be directed into the rich gas main, and at a later time when the gases are relatively lean connection will be made with the lean gas main so that the during this period will pass through that main rather than through the rich main,

The gases in each of the collector mains are cooled independently and to a regulated extent by the application of sprays of ammonia liquor or ammonia liquor and tar thereto for the purpose of reducing the temperature and flushing the main to prevent the accun'iuiation of tar or pitch in the main and the distillation of such accumulated matter to coke. The dew points of the gases for the several constituents carried therein as vapor are lower than the normal boiling points of these constituents and by suitable regulation of the temperature or the gases in the collector mains it is possible to eiiect the condensation of all or any desired part of the vapors carried by the gases into the liquid phase. Any desirable imcondensed vapors can be recovered-1n the condensingsystem. To accomplish the intended purpose the temperature of the. gases should'be main-v tained above the dew points of the gases for all constituents which it is desired to retain in the gases and car y over therebyafter the separation of hea y oils therefrom 1n the collector main.

Some of the tarry or pitch constituents which are condensed by the cooling effect of the ammonia liquor separate in the respective collector mains and can be withdrawn therefrom together with the ammonia liquor employed for cooling. The balance of the tarry and pitchy constituents in the gases willbe carried from the collector main by the gases and will be recovered with the oils in the condensers or may be removed from the gases by a cleaning treatment so that on cooling the cleaned gases clean oils will be produced. The mixtures of tar and am- -will be volatilized.

monia liquor from the collector mains are treated in suitable decanters to separate the ammonia liquor from the tars. Diiierent tars are obtained from the rich and lean gas mains which can be separately distilled to produce distinctive pitches.

According to this invention I set aside a portion of the rich or lean gas collector main for the distillation of tar. A portion of one or both of the collector mains is set aside by diaphragms or other suitable means preferably disposed in a section of the main adjacent to the centre box and forming a section in which tar can he distilled and pitch can be accumulated separately from the ammonia liquor and the tar which flows thru the balance of the main as a result of cooling the gases by spraying with a cooling medium such as ammonia liquor or tar and ammonia liquor.

The tar to be distilled may be introduced to the section of the collector main set aside for distilla ion, preferably through spray nozzles pro'i'ii'led for that purpose. Suitable agitating or spraying means may be provided in the main by which the tar is intimately mingled with the hot gases in this portion 01'' the main and subjected to the distilling efi'ect thereof whereby volatile oil constituents are distilled from the tar and join. the coal distillation gases passing from the main.

The extent to which the tar is distilled may be varied by varying the intimacy 0'! contact between. the tar and the hot gases. Only lower boiling constituents of the tar will be distilled if the tar is allowed merely to flow thru the bottom of that section of the main which is set aside for the distillation of tar. If the tar is admitted to the main thru spray nozzles, or it the tar in the main is sprayed up into the gases by a suitable agitating device, higher boiling oils By proper regulation of the distillation, a pitch of desired melting point may be produced. For certain road construction purposes, for example, a pitch with a melting point in the neighborhood of 105-110 F. and a free carbon content of around 10 to 15% or higher, is required. Such a pitch maybe produced at a coke oven plant by separately collecting a tar of correct carbon content in the lean gas main and distilling this tar to a pitch of the required melting point by flushing it thru the bottom of that section oi. the lean gas main set aside for distillation, or spraying it into the gases in this main. The pitch recovered may be recirculated thru the distillation portion of the main where suliicient distillation is not obtained on the first passage of the tar thru that portion of the main set aside for distillation. The character of the pitch produced may be varied by modifying the treatment thereof with respect to the/amount, of tar introduced into the distillation section of the main, the time during which it is exposed to the hot gases and the temperature of the gases employed for distillation. I

Some of the tar and pitch constituent-s may be retained in the gases leaving the collector main as globules or as tar fog. \Vhere clean oils are desired such entrained matter may be removed from the gases in a gas scrubber or an electrical precipitator; A precipitator of the Cottrell type may satisfactorily be employed and it should be operated at a temperature such as to avoid the condenastion of desired oils before the gases leave the precipitator. Consequently the precipitator should be disposed preferably closely adjacent to the collector main and the gases carrying the pitch constituents should be delivered directly thereto. The electrical precipitator may advantageously be insulated to prevent loss of heat from the gases. This is particularly desirable if theproduct to be recovered comprises relatively high boiling oils requiring the maintenance of the ses at high temperature to avoid dilution of the pitch thrown down in the precipitator with oil constituents.

Separate tars may be distilled in each of the two or'1nore mains of the battery and the gases and vapors from each of the mains may be cleaned in separate .precipitators to produce separate oil products or the gases may be combined to produce one clean oil fraction.

The operation of the electrical precipitator as commonly used consists in passing the gas to be treated between electrodes whose difference in electrical potention is very great. 7 to use a rectified alternating current. The alternating current (the primary) is sent thru a step-up transformer to produce a high potential current (the secondary) which is then rectified to an intermittent uni-directional current, for example, by means of a rotary converter. The rectified current is delivered from the converter to the electrical precipitator at practically the potential at which it leaves the transformer.

The electrical precipitator as commonly used consists essentially of a group of vertical pipes with a wire or rod in the centre of each, the pipes being connected to proper hemlers for the introduction and discharge of the gases. The pipes generally constitute the positive electrodes and the wires orrods the negative electrodes. The size of the pipes may vary, but in general pipes of less than six inches in diameter are not em ployed. Electrical precipitators with pipes six inches in diameter using secondary volt ages of from 35,000 to 50,000 Volts are satisfactory for the purposes of this invention.

Experience has shown that it is best i It is generally. best to operate with maxiupon several variables. Satisfactory cleaning of the gas may be accomplished if the time of treatment 1s of the order of one second although this time may be varied widely.

depending upon the character of the pitch to be recovered from the gases passing through the precipitator. In working wlth tubes vnine feetlong and six inches in diameter,

for example, substantially all of the tarry constituents have been separated with a time of treatment of from one and one-half to two seconds, or with a gas velocity of from six to 4.5 feet per second. This gives an eihciency of cleaning of approximatly ninety-n1ne percent. A shorter treatment of, for example, from 0.5 to one second corresponding toa gas velocity of from eighteen to nine feet per second may result in the passage of some of the tarry constituents through the precipitator.

From the. gases carrying the condensable vapors can be conducted through suitable condensing apparatus including coolers, scrubbers, fractional, condensers, fractionating columns, etc., devised to reduce the temperature of the gases and to cause the separation of oils therefrom. One total oil fraction may be collected if the gases are cooled in one step to the lowest desired temperature. Several oil fractions canbe recovered if the gases are cooled by stages in coolers designed for separate collection of the oils corresponding to the individual cooling steps.

Electrical precipitators of the type employed for initial separation of pitch from thegases may be used to separate the condensed vapors. By passing the through such precipitators at predetermined temperatures the condensed constituents can be separated effectively and sharp cuts of oil can beobtained. The gases, after the successive condensations accompanied by separation of the oil constituents, can be conducted through the usual equipment provided for the purpose ofrecovering other valuable constituents such as ammonia and light oils therefrom.-

Inthe practice of the present invention the cooling of the rich and lean gases in the separate collector mains .may be regulated electrical precipitators the gases by supplying more or less ammonia liquor or other cooling agent thereto forthe purpose of determining the character of the pitches which will be separated in the electrical precipitators connected to the separate collector mains and by such regulation the amount of the tar and oil constituents which are condensed in the collector mains and separated in the electrical precipitators may be regulated to produce pitches having different melting points and other characteristics. The pitch recovered by th treatment of the rich gases in an electrical precipitator will, however, be a low free carbon pitch whereas the pitch recovered from the treatment of the lean gases will be a high free carbon pitch, and these pitches may be distilled in the rich or lean gases or may be otherwise utilized for the various purposes for which they are adapted, the melting point of the particular product being adjustable by the regulation of the cool- "ing in the separate collector mains as hereinbefore described.

While the invention is designed primarily for the distillation of the tar separated in the cooling sections of the collector mains,

-it is to be understood that the distillation sections thereof may be varied in size to per mit the distillation of additional quantities of tar derived from other sources as, for example, from other coke ovens, from gas 35 retorts, from vertical retorts, or from watergas sets. The tar from other sources may be mingled with the tar from the coke-oven battery or it may be distilled separately to produce products distinct from those recovered in the electrical precipitators.

The invention may be applied to existing coke-oven plants without any considerable modification thereof except for the provision of two or more collector'mains connected to all of the ovens of the batter], one or more of which is provided with diaphragms as herein described. Where the coke-oven plant is already equipped with separate collector mains substantially the only modification required is the introduction of separate tar collecting means, the introduction of diaphragms and the installation of electrical precipitators or other cleaning means whereclean oils are desired.

The present invention is of more or less general application to coke-oven plants and to the recovery of pitches and oils from the gases dischargedtherefrom. It will be further described with reference to the ac'com panying drawings, but it is intended and will be understood that the invention is not limited to the specific details of the apparatus as illustrated in the drawings, in which Fig. 1 is a plan view of a portion of the "cohe-oven battery illustrating the application of the invention thereto;

Fig. 2 is an enlarged sectional view showing the separate collect-or mains and electrical precipitator Fig. 3 is a detail in section of the electrical precipitator;

Fig. 4 is a longitudinal section through one of the'collector mains indicating the arrangement of the diaphragms therein to provide the distillation zones; and

. mains will pass from these Fig. 5 is a schematic view showing six collector mains of a coke oven battery and one condensing system Without electrical precipitators or other means for cleaning the gases.

Referring to the drawings, 5 indicates the battery of ovens-which are connected by uptake pipes and goose-necks 6 to valve boxes 7' which con'miunicate with the collector mains SR and SL. The collector main 8R is the main for collecting the rich gases and the collector main SL is the main for collecting the lean gases which are given of]? from the ovens during the latter portion of the coking cycle. In the drawings, identical pieces of apparatus used in connection with both the lean and rich gases are indicated by the same reference numeral with the sullix L or respectively.

Valves 10 are arranged in the valve boxes to permit the direction. of the hot coke oven gases into one or the other of the collector mains, depending upon the stage of the coal distillati m operation in the particular oven to which the valve box is connected. In F ig. 2 the valve box in the collector main for the rich ases SR is closed so that the gases from th oven to which uptake 6 is connected pass thru the valve box into the collector main (or the lean gases 8L. Thus, by operating the valves during the coking operation .rich and lean gases from the ovens of the battery can be collected separately in the two collector mains. lVhen one desires to collect richest or leanest gases or specially blended independently of any other, a third collector main may be advantageously employed to collect the balance of the gases.

The gases are cooled to the desired extent in the c llcctor mains by ammonia liquor or ammonia liquor and tar introduced thru spray nozzles 11 which are supplied thru a pump 12 and pipe 13 from a source which, in the drawings, is indicated by the source of ammonia liquor 1%. The amount of cooling medium supplied to the separate collector mains will depend upon the extent to which the gases are to be cooled. The cooling will be so regulated that constituents desired in the products obtained from the collector mains will be thrown down in the collector mains and products which it is desired should pass from the collector mains with the gases either as vapors or as particles of liquor entrained in the gases.

Where clean oils are desired as a product of the operation, the gases leaving the collector mains may be cleaned. in the electrical precipitators or other suitable cleaning means and the condensable constituents of the gases passing thru the cleaning means in vapor form may thereafter be recovered as clean oils by cooling the gases passing therefrom. I

Fig.1 shows an arrangement in which the gases from the two collector mains are separately treated to remove entrained par ticles and are thereafter separately cooled to condense separate clean oils. The gases from the collector mains 8B and 8L which carry oil vapors and entrained tarry and pitchy particles, are passed thru the pipes 16L and 16R to the electrical precipitators.

These comprise casings 18 enclosing a number of tubes 19 which are supported in the heads 20 and 21 within the casings. In each precipitator an inlet for the gases near the bottom of the casing communicates with a chamber 23 which is partially separated from the tube section by the baflle 2 1. An outlet 25 permits the escape of gases from the precipitator after the gases have passed thru the tubes.

. Each precipitator is provided with a plurality of electrodes 26 preferably in the form of metal rods which extend thru the tubes and are supported from a bus-bar 27 located near the upper ends of the tubes. The busbar 27 extends at both ends into casings 28 which include insulators 29 upon which the bus-bar is supported. The high tension current line extends into the casing 28 and connects with the bus-bar 27, thus supplying the necessary current from any suitable source of uni-directional current under high tension. The casing of the separator is grounded or otherwise connected to the source of current to complete the circuit. The casing andtubes form the positive electrode, the electrodes connected to the bus bar being negative. The form and arrangement of the conductors in the circuit can be varied. The arrangement should be such as to supply high tension uni-directional current to the electrodes, thereby permitting a continuous silent discharge between the electrodes and the tubes from which the gases ass.

The gases carrying tar in the form of globules or tar fog together with solid particles such as carbon, etc, in finely di' vided form, enter the precipitators from the mains 16L and 16R and pass thru the tubes of the precipitators, being subjected therein to the electrical discharge which thru ionization of the solid and liquid particles causes them to separate from the gases and condensable vapors. The separated liquid together with the solid particles run down the inner walls of the tubes into the chambers at the bottom of the precipitator and can be withdrawn thru pipes 30L and 30B and delivered to suitable receptacles 31L and 31B; at relatively low temperatures they will serve as decanters; at relatively high temperatures e.g. 125-150 C. and upwards they will serveas collectors for pitches of 105- 115 F. melting point. The tars or pitches as the case may be may be run to tanks indicated and recirculated to the stills or not as desired. 7

The gases carrying the condensable vapors escape thru the outlets 25 of the precipitators and are delivered through pipes 32L and 82B to condensers 33L and 33B. The condensers may be of any suitable form and in the present instance I have shown condensers of the ordinary direct or wet type which are employed commonly in by-product recovery systems. The gases and vapors are cooled therein by contact with grid surfaces wet by the sprays of ammonia liquor, for example, and the resulting condensates are withdrawn thru pipes 34L and 34B to decanters 35L and 35B wherein the oils are separated from the ammonia liquor. The. gases are withdrawn from the condensers thru the pipes ESL and 36R and delivered to exhausters Twhich' maintain the pressure balance in the systems. The gases may be conducted from the exhausters to the. usual equipment for the recovery of ammonia, light oil, etc., therefrom.

Ammonia liquor and the tar which separate inthe collector mains may be withdrawn thru pipes SSL and 38R connected to the ends of the mains. This may be delivered to decanters 40L and .lOR wherein the ammonia liquor is separated from the tar. The ammonia liquor may pass thru a pipe 41 to the storage tank 14 whence it may be returned in part thru the pipe 13 by the pump 12 to the spray nozzles in the collector mains hereinbeforedescribed to provide for the cooling of further quantities of gases in the collector mains. The tar from the collector mains may be delivered to the storage tanks 45R and 45L where the 'low carbon tar from the rich gases and the high carbon tar from the lean gases will be-separately collected.

According to this invention the tar from the gases from a selected portion of the coking period is returned to one of the collector mains by a pump 46, thru av main 47 and sprays 48 and distilled by the heat of the gases in this collector main. Preferably the tar is returned for distillation to the same collector main in which it has previously been separated from the gases. A selected portion oi the main is separated from the balance of the main for this distillation so that the heavy tar or pitch resulting from the distillation may be drawn oil' from the main separately from the tar and ammonia liquor present in the balance of the main. distillation is advantageously located near the center-box of the collector main, i.e., near the point at which the gases are taken off from the main and sent to the condensers,

or where cleaning is effected, to the precipi- The portion of the main set aside for tators or other cleaning apparatus. When the distillation portion of the main isset aside near the cross over main the vapors resulting from the distillation are swept from the main by the other gases which ordinarily will be gases which have been sprayed with ammonia liquor or ammonia liquor and tar gree of cooling of the gases with ammonia liquor will be regulated to the required extent to allow distillation of tar in the section of the main devoted to distillation to progress to the desired degree. Excessive cooling of the gases would, result in excessively lowering the temperature of the gases in the distilling section.

. In Figs. 1 to 4 of the drawings each col lector main is provided with a distilling zone separated from the balance of the main by the diaphragms 49 which prevent the pitch produced in the distillation zone from mingling with the tar and ammonia liquor and the adjacent cooling sections of the mains. In the drawings spray nozzles 48 are shown for spraying the tar into the hot gases in the distillation zone. Where one spraying of the tar into the gases is not suflicient to produce the distillation required, the partially distilled tar drawn off from the distillation zone may be resprayed into the gases for further distillation. Similarly, agitating means such as paddles or discs or rapidly rotating rolls may be situated in the main in such a way as to throw the tar from the bottom of the main up into the gases to produce the desired distillation. VVhere mere topping of the tar is all that is required, the tar may be allowed to flow, thru the bottom portion of the main without intimate mingling of the tar with the gases and limited distillation will result. The pitch which is formed in the distillation zone of each collector main, where each main is employed for the distillation of tar, may be withdrawn thru a. pipe 50 and delivered to a storage receptacle 51. If desired, all or a part of the pitch can be recirculated by means of a pump 52 and pipe 53 and delivered thru the pipe 47 and spray nozzles 48 for further heating and distillation in the distillation zones of the respective col lector mains.

The gases leaving the main contain vapors originally present in the gases as they left the ovens and vapors resulting from the dis tillation of the tar in the main and also tar fog, and particles of'pitch where tar has been brought into intimate contact With I is separated in the precipitator includes such residue from the distillation of tar.

The clean OllS recovered 1n the condensers and 33L will vary in composition, de-

pending upon the different constituents pres ent in the gases given ofi" during the early and the later portions of the coking opera tion and also depending upon the nature of the tar distilled and the quantity of vapors distilled from the tar and carried thru the precipitator and into the condensers.

Where clean oils are not especially desirable, the tar recovered from one or the other of the mains may be distilled by intimate contact with the hot gases in one of the mains and the pitch thus produced recovered and kept separate from the tar from the balance of that main and the tar from the other main, or both mains may be employed forthe distillation of tar. The gases from both of the collector mains may be united and together condensed in one condenser. Fig. 5 shows in a schematic way means adapted for the production of a high carbon tar suitable for use on roads and the simultaneous production of other tar which may be distilled to produce distillate oils.

According to the arrangement shown in Fig. 5, the rich and lean gases from a bat tery of, for example, 60 ovens may be separately collected in three rich gas and three lean gas collector mains SR and 8L. A portion, approximately one-half, of each of the lean gas mains is equipped for the distillation of tar. The drawings show means by which the tar from the balance of the lean gas mains, which is high carbon tar, is withdrawn thru the pipes 38L to the storage receptacle 40L. This tar is conveyed thru the pipes 47L and sprayed into the gases in the selected portions of the lean gas mains set aside from the balance of the mains by the diaphragm 49. The residue from the distillation which is the high carbon pitch desired is Withdrawn into the receivers 51L and if desired is recirculated thru pump and line 47L for further distillation. The gases from the lean gas mains enriched by vapors resulting from the distillation of tar in these mains pass from the collector mains thru the mains 16L and are united. with the gases from the rich collector mains passing thru the mains 16R. Together the gases are cooled in the condensers 33 where a total tarry oil fraction is collected which differs from the ordinary tarry oils usually recovered in the condensers in that it is enriched in oils distilled from the high carbon tar in the collector main for the lean gases and is somewhat deficient in lean gas tar.

The drawings and 7 description have shown the diaphragm so placed as to cause the distillation to be conducted in a compartment adjacent the center box. This is not essential. The distillation compartment may be located adjacent the extreme end of the main in wiich lines 38 and as well as 47 and 13 and nozzles 11. and 48 will be interchanged in order to deliver products to the proper tanks as shown. WVith such an arrangement, hard pitches can be made in the distilling section and yet the temperatures in the other section may be held down to normal if desired, or may likewise be more elevated.

The greater proportion of the heavy oils distilled may, if desired, be thrown down with the tar in the section oi the lnain not devoted to distillation, or by raising the main temperature a less proportion may be thrown down. Thus a greater or less amount of the heavier oils may, as desired, be thrown down or may be allowed to pass to the condensers.

By regulating the ratio of the high carbon tar distilled by the hot gases, the time of contact, the intimacy of the contact between the tar and the gases, etc, the distillation can be controlled to produce a pitch of required melting point. By regulating both the proportion of the gases collected in the lean main and the distillation of the tar thus obtained, both the carbon content and the melting point can be controlled. The high. carben tar from the lean gas main may be' blended with high carbon tar from other coke oven batteries or other sources when this is desirable.

Although the invention is described more particularly as applied to a coal distillation plant equipped with two collector mains,

more mains may be employed, where this is desirable to obtain gases from any selected traction or fractions of the coking cycle to obtain tar and then pitch of a desired free carbon content. I

Although the invention is more particu larly adapted to the product? on of high carbon pitches at coalv distillation plants, and especially at coke oven. plants, by the distillation of tar recovered from the gases during the later portion of the coal distillation cycle by contact with fresh iot coal distillation gases, it may be applied more generally for the production of various pitches by distilling either high or low carbon tars from the early or later portions of the coking cycle. The gases resulting from the distillationoi tar will blend with the ordinary gases and the rich and lean gases from the collector mains enriched in vapors resulting from the distillation may be united and condensed to produce a total tar product, or they may be separately cleaned to produce separate clean oil fractions or they may be cleaned and united to produce one total clean oil fraction. of varying properties may be produced from the precipitators. These and other advantages of the invention may be attained by the practice of the principles as herein set forth, it being understood that various changes may be made in details of the operation and the apparatus as described with out departing from the invention or sacrifieing the advantages thereof.

I claim:

l. The method of operating the by-product recovery system of a coal distillation plant which comprises separately collecting the hot coal distillation gases from the earlier and the later stages of the coking operation in individual ovens or retorts of the plant, separately cooling a portion of the gases from one stage to separate tar therefrom, separately collecting the tar and bringing it int-o intimate contact with another portionof the hot gases from the same stage whereby it is distilled, collecting the cool portion of the gases and the gases and vapors resulting from the distillation together, and collecting the residue from the distillation separately from the tar.

2. The method of producing high carbon. pitchwhich comprises separately collecting in one collector main the hot lean gases given oil during the later part of the coking operationin various ovens of a coke oven battery in the. ovens of which coal is being coked, separately cooling a portion of these gases and regulating the cooling to obtain a high carbon tar, withdrawing from the main the high carbon tar and distilling this tar in another portion of the hot lean gases in the main to produce high carbon pitch, blending vapors from the distillation with the cooled gases and withdrawing them from the main and cooling them, and withdrawing from the main the high carbon pitch separately from the tar.

3. The method of operating the by-product recovery system of a coal distillation plant, which comprises separately collecting the hot coal distillation gases from the earlier and later stages of the coking operation inv individual ovens or retorts of the plant, cooling a portion of the gases of one stage to separate tar therefrom, separately collect-- ing the tar and bringing it into intimate contact with another portion of the hot gases from the same stage whereby it is distilled, combining the cooled portion of the gases and the gases and vapors resulting from the distillation, collecting the resi due from the distillation separately from the tar.

STUART PARMELEE MILLER.

Desirable pitches I 

